The U.S. Federal Communications Commission has fined Verizon US$3.4 million over its failure to notify police and fire departments during a 911 service outage last year.

Under the commission’s rules, Verizon and other carriers were required to notify emergency call centers of a six-hour outage that occurred in April. The outage involved multiple carriers and affected over 11 million people in seven states.

Verizon’s portion affected 750,000 California residents who were unable to call 911 to reach an emergency operator at 13 call centers in northern California. The outage was the result of a coding error at a large 911 routing center.

“Americans must have confidence that they will be able to reach 911 in an emergency,” FCC Chairman Tom Wheeler said in a statement Wednesday.

Under terms of the settlement, Verizon also has to identify and protect against risks that could lead to 911 service disruptions.

“We take the safety of our customers and the service we provide to 911 centers and first responders very seriously,” a Verizon spokesman said in an emailed statement. “We will continue to work with our partners to meet the standards our customers expect from Verizon,” he said.

The problems started just before midnight Pacific Time on April 9 and affected 911 callers seven states—California, Florida, Minnesota, North Carolina, Pennsylvania, South Carolina, and Washington. Over 6,600 911 calls never reached a call center.

“Although, fortunately, it appears that no one died as a result, the incident—and the flaws it revealed—is simply unacceptable. Americans rely on 911 as a reliable way to communicate in an emergency, and lapses like this cannot be permitted,” the FCC said in a report on the incident in October..

Late last year, the FCC began work on new rules to improve consumer choice and access to emergency call services as the U.S. shifts from copper-based networks to IP networks.